SiC-containing fibers are more particularly used in the fields of aviation, aerospace supplies and of surface vehicles as reinforcement fibers for composite materials, and more particularly the composite materials having a ceramic matrix (C.M.C.)
The thermal and mechanical properties of these composite materials above all depend on the properties of the fiber reinforcement, (for instance, fibers containing aluminum oxide or silicon carbide) and of a matrix/fiber interfaces. As a rule, the strength of fiber solids having some degree of brittleness is widely dependent on the presence of surface defects. They require a fiber surface protection during the production and use of CMC.
From a chemical point of view, a ceramic fiber is normally exposed to the action of four different chemical media:
the reactants which are used to form the matrix according to a processing method involving liquid or gas phases, PA1 the ceramic matrix, PA1 the interphase that can be resorted to control the fiber/matrix bonding and to obtain a high toughness, and PA1 the gas atmosphere (air, for instance)
According to their nature, the above media can react with the fibers at high temperature and cause a decrease of the reinforcing capability thereof.
These reactions may cause serious alterations in the fiber surface defects, enlarging some existing defects or creating new ones, and thereby they reduce the failure strength of the fiber.
In order to protect the fibers against these reactions and also to improve their mechanical properties and make them less dependent towards the matrix, it is known to coat the fiber surface with a layer that forms an interphase. For instance, this interphase may be a pyrocarbon or a hexagonal boron nitride. In some cases, when the production of the composite material requires sufficiently high temperatures, the interphase may be created during the production process of the composite material. In this way, a carbon interphase is created in composite materials having a matrix of lithium aluminosilicate with SiC-containing reinforcement fiber. (J. J. BRENNAN Tailoring Multiphase and Composite Ceramics, Material Science Research, RE. TESSLER and al. p. 549-560, Plenum Press, New York, 1986).
However, the use of these deposits is not entirely satisfactory more particularly in the case of composite materials obtained by the soil/gel process.
Now, the Applicant has been able to develop a processing method for a silicon and carbon containing ceramic fiber and more particularly a SiC-containing ceramic fiber having for its purpose to eliminate the disadvantages of the previous art and to create an external carbon coating.